1. Field of the Invention
The invention relates in general to switching circuitry for driving plasma display panels (PDPs), and more particularly to a method and an apparatus for driving plasma display panels to enhance the luminous efficiency.
2. Description of the Related Art
AC plasma display panels (ACPDPs) have the following advantages: large screens, wide viewing angle, large capacity, and the ability to display full-color images, However, their disadvantage of high power consumption needs to be overcome. In order to improve the efficiency of AC-PDPs, energy recovery is a necessary function of the driving circuit of the plasma display panels. Moreover, modifying the sustaining waveform for driving ACPDPs is an alternative way to improve the luminous efficiency.
The driving waveform of AC-PDPs essentially has three periods: a reset period, a write (address) period, and a sustain discharge period. To ensure the accuracy of addressing, an erase pulse is applied during the reset period, and the wall charges in all discharge cells are cleared. In the write period, the discharge cells of ACPDP are selected according to the display image data to write and therefore the wall charges exist in the ON cells. As a result of the wall charge""s memory effect, the selected discharge cells discharge to emit light pulses continuously as long as a moderate alternating voltage is applied between the sustain electrodes X and Y during the sustain discharge period.
In FIG. 1, a conventional sustaining waveform and the corresponding light emitting pulses are shown. The horizontal axis represents the time. The vertical axis represents the applied voltage between the sustain electrodes X and Y, which is denoted by Vxy, and the light emitting power. At t1, t2, and t3, during which the wall voltage plus the applied voltage exceeds a firing voltage, light emitting pulses are generated.
Discharging current is one of the factors influencing the luminance and the luminous efficiency of AC-PDPs. As disclosed in xe2x80x9cBasic Study on the Gas-Discharge Panel for Luminescent Color Displayxe2x80x9d, IEEE Trans. Electron Devices, vol. 25, pp.1094-1100, 1978 by T. Kamegaya, H. Matsuzaki, M. Yokozawa, the luminance reaches saturation and the luminous efficiency decreases as the discharging current reaches to a critical value. Thus, by choosing appropriate operating points of the discharge current, higher luminous efficiency can be obtained.
FIG. 2 is another sustaining waveform differed from the one in FIG. 1. The horizontal axis represents time. The vertical axis represents the applied voltage Vxy and the light emitting power. As disclosed in xe2x80x9cImprovement of Luminous efficiency in an ACPDP by Self-Erase Discharge Waveformxe2x80x9d, SID""99 Digest, pp. 540-543, 1999, by T. Hashimoto, A. Iwata, a self-erase discharge is applied to lower the main discharging and therefore, the luminous efficiency is improved. The self-erase discharge can be improved by decreasing the falling rate and the pulse width of the sustain voltage and by applying an assistant pulse to the ACPDP. For example, the assistant pulses are applied at t1, t3, t5, and t7. The assistant pulse applied at t1 has a period of T1 and an amplitude of V1 in FIG. 2. Consequently, the self-erase discharge occurs at t1, t3, t5, and t7 while the main discharge occurs at t2, t4, and t6. Before the main discharge, the wall charge is reduced because of the self-erase discharge. However, the assistant pulses will attract the space charge produced by the self-erase discharge and even make the main discharge too weak if the period of the assistant pulse is too long. As a result, the sustaining frequency must be high and the margin of the sustain voltage becomes narrow. Additionally, according to the previous experiments the luminous efficiency is reduced when the sustaining frequency is higher.
It is therefore an object of the invention to provide a method and an apparatus for driving plasma display panel to improve the luminous efficiency with power recovery. The proposed sustaining waveform can be operated at the appropriate frequency to get a large sustain voltage margin. Under an experiment of a 42-inch ACPDP, the luminous efficiency is enhanced by more than 30%.
The invention achieves the above-identified objects by providing a method for sustaining discharging in the discharge cells of a plasma display panel (PDP) having first sustain electrodes, second sustain electrodes, and address electrodes. The first sustain electrodes are arranged in parallel with the second sustain electrodes. The address electrodes are arranged orthogonal to the first sustain electrodes and said second electrodes. The first sustain electrodes and the second sustain electrodes intersect with the address electrodes to form intersections which define discharge cells that can be selectively turned ON and OFF. First, a first pulse of a first positive voltage is applied between the first sustain electrodes and the second sustain electrodes. Next, the voltage between the first sustain electrodes and the second sustain electrodes maintains at a second positive voltage for a first period. Then, a second pulse of a third positive voltage is applied between the first sustain electrodes and the second sustain electrodes. After that, a third pulse of a first negative voltage is applied between the first sustain electrodes and the second sustain electrodes. Then, the voltage between the first sustain electrodes and the second sustain electrodes maintains at a second negative for a second period. Finally, a fourth pulse of a third negative voltage is applied between the first sustain electrodes and the second sustain electrodes. The second positive voltage is lower than the first positive voltage and the third positive voltage, and the second negative voltage is higher than the first negative voltage and the third negative voltage.
It is therefore another object to provide an apparatus for providing sustaining waveform to a discharge cell of a plasma display panel (PDP). The selected discharge cell is defined by a first sustain electrode, a second sustain electrode which is parallel to the first sustain electrode, and an address electrode which is orthogonal to the first sustain electrode and second sustain electrode. The apparatus includes a first energy recovery circuit, a second energy recovery circuit, a first capacitor and a ninth switch, and a second capacitor and a tenth switch. The first energy recovery circuit, which includes a first inductor and four switches, is connected to the first sustain electrode. In the first energy recovery circuit, A first switch is connected between the first sustain electrode and a power supply. A second switch is connected between the first sustain electrode and ground. A first inductor is connected between the first sustain electrode and a first node. A third switch is connected between the first node and the power supply. A fourth switch is connected between the first node and ground. The second energy recovery circuit is connected to the second sustain electrode. The second energy recovery circuit includes a second inductor and another four switches. The fifth switch is connected between the second sustain electrode and the power supply. The sixth switch is connected between the second sustain electrode and ground. The second inductorA is connected between the second sustain electrode and a second node. The seventh switch is connected between the second node and the power supply. The eighth switch is connected between the second node and ground. Moreover, the first capacitor and the ninth switch are connected in series between the first sustain electrode and the first node, and the second capacitor and the tenth switch are connected in series between the second sustain electrode and the second node.